In order to reduce the pollutant emissions in vehicles with diesel drive, a reactant, for example, a urea/water solution, is mixed into the exhaust gas flowing in an exhaust gas-carrying duct of an exhaust system. In order to obtain a good mixing of the reactant, which is injected by means of a reactant injector unit, also generally called an injector, with the exhaust gas, it is known to arrange a mixer, which generally has a plurality of deflecting surfaces arranged inclined toward the exhaust gas flow direction, in the exhaust gas-carrying duct that is arranged downstream of the injection site. The exhaust gas and the reactant impinge on these deflecting surfaces and are deflected there, so that improved mixing is achieved due to the swirling developing in this connection. At the same time, the deflecting surfaces of such a mixer, which are heated by the exhaust gas, support the heating and the evaporation of the reactant impinging thereon and injected in droplet form into the exhaust gas.